Having a disaster recovery plan in place before a disaster happens is critical to the long term success of your tank. It is very easy to invest over $10,000 into a reef tank over several years and lose everything because you did not spend a few hundred for the "Just in case". Most tank disasters are not related to life threatening events. I'm not talking about earthquakes, tornados or meteor impacts. In such cases you have more to worry about than a fish tank. I'm talking about loosing power for a hours to a few days either due to ice storms, car hitting a pole, local energy shortage, etc.

In most cases a tank can go for about an hour or so with no power with little effect. However, once you start reaching around 45 minutes into a power outage you should start your disaster recovery plan. If you reach the point where worms are crawling out of your sand bed to get air you have likely waited to long and are in for a rough ride.

Depending on season you have two primary factors to worry about in reef tanks temperature and oxygen levels.

Calcium reactors or calcium carbonate reactors have been in the hobby a long time, our German hobbiest counterparts have been using them since at least 1994 to support their SPS tanks.

Many people including myself try to maintain calcium and alkalinity levels in their tanks with kalkwasser and/or two part additives. And for many people this works very well. Eventually each of us progress into the world of Tridacnid clams and SPS corals and start having trouble keeping their calcium and alkalinity levels elevated. And as someone who has made 3 to 5 gallons of kalkwasser every single night its a relief to get away from it.  The most basic way to describe how a calcium reactor works is this: It is the reverse process of calcification. Carbon Dioxide gas is used to create carbonic acid which dissolves a calcium carbonate media. This in turn creates calcium ions (Ca++) and bicarbonate ions (HCO3-). Best of all its added in a balanced proportion that is used in calcification.

The formula commonly used to describe this process is:

CaCO3 + H2O + CO2 <-> Ca2+ + 2HCO3-